1. Field of the Invention
The present invention relates to decorating apparatus for decorating an object, particularly, a circular object, and in a particular application, for decorating a can, and particularly to a digital can decorating apparatus for digitally controlled printing on two-piece cans. Although the disclosure herein describes the invention as applied to decoration of cans, the invention is applicable to decorating any object, and particularly a generally cylindrical or round object which is adapted to be supported, and particularly rotated, in opposition to a blanket segment that has been printed by a digitally controlled device.
2. The Prior Art
Conventionally, two-piece cans are decorated by offset printing. In such a process each color ink is contained in a separate inking station that transfers the ink to a printing plate. The ink on the plate is transferred to spaced apart blanket section of a printing blanket that is rotated past all the inkers. The complete patterns of inks are then simultaneously applied from each blanket section to the can then in register with that inked section of the blanket. If a different image is desired to be printed, or a change is desired in the image, it is necessary to change each printing plate of each inker, which plate transfers to the blanket a particular image and color which has been assigned to that inker. When the ink color provided at an inking station is to be changed, the ink distribution rolls of the inker must be cleaned to avoid contamination of the new color by the previous color. A representation of such a known device, including conventional inkers, is shown in FIG. 1.
Further examples of similar can printing devices are shown in U.S. Pat. Nos. 3,766,851, 5,799,574 and 6,367,380. U.S. Pat. No. 5,799,574 discloses a relatively high speed apparatus for applying decorations to the exterior of cylindrical containers while they are mounted on mandrels which are disposed along a periphery of a large continuously rotating disk carrier. Decorations are applied to the containers as they engage a rotating blanket of a decorator that is adjacent the periphery of the carrier. During engagement between the containers and the blanket, the containers track the blanket surface through the printing region where the containers and the blanket surface are engaged.
This type of decorating equipment includes a number of relatively heavy elements that move at high speed.
Major components of this decorating apparatus comprise separate inkers, at least one for each ink color. Each inker is comprised of an ink supply followed by a series of ink distribution rollers, as in U.S. Pat. Nos. 6,367,380; and 5,186,100 or other ink distribution designs within an inker, as in U.S. Pat. No. 6,367,380. Each inker is heavy and complicated as it is comprised of many elements. Because there must be precise coordination between the various elements, inertia forces and operating power are significant engineering design considerations, as are equipment down time, maintenance, cost and setup procedures.
Digital printing is used in many environments. Digital printing might be broadly defined as printing without use of printing plates. An example of digital printing is ink jet printing, of which there are several different techniques, including the use of a piezo element to apply pressure to a nozzle chamber to force a drop of ink onto a medium, continuous ink supply with required ink droplets channeled onto the medium, thermal printing where a gas bubble in a nozzle chamber creates pressure forcing an ink droplet onto the medium, or ink in solid form is melted as needed and then applied like a liquid ink jet. Ink might be sprayed by a spray jet. Other non-plate techniques of applying ink include thermal wax or resin tracer, dye sublimation, etc. Use of a particular technique of digital printing is not required for performance of the present invention. Ink jet printing overrides the various steps and apparatus associated with producing, mounting and setting printing plates and avoids need for conventional inkers and avoids having to clean distribution rollers of the conventional inkers.
Apparatus for adapting the digital printing technique to decorating of cans or containers, and of the type of the present invention, have not previously been disclosed.